/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.servlet.jsp.tagext;

import java.io.IOException;
import java.io.Writer;
import javax.servlet.jsp.*;

/**
 * Encapsulates a portion of JSP code in an object that can be invoked as many
 * times as needed. JSP Fragments are defined using JSP syntax as the body of a
 * tag for an invocation to a SimpleTag handler, or as the body of a
 * &lt;jsp:attribute&gt; standard action specifying the value of an attribute
 * that is declared as a fragment, or to be of type JspFragment in the TLD.
 * <p>
 * The definition of the JSP fragment must only contain template text and JSP
 * action elements. In other words, it must not contain scriptlets or scriptlet
 * expressions. At translation time, the container generates an implementation
 * of the JspFragment abstract class capable of executing the defined fragment.
 * <p>
 * A tag handler can invoke the fragment zero or more times, or pass it along to
 * other tags, before returning. To communicate values to/from a JSP fragment,
 * tag handlers store/retrieve values in the JspContext associated with the
 * fragment.
 * <p>
 * Note that tag library developers and page authors should not generate
 * JspFragment implementations manually.
 * <p>
 * <i>Implementation Note</i>: It is not necessary to generate a separate class
 * for each fragment. One possible implementation is to generate a single helper
 * class for each page that implements JspFragment. Upon construction, a
 * discriminator can be passed to select which fragment that instance will
 * execute.
 * 
 * @since 2.0
 */
public abstract class JspFragment {

	/**
	 * Executes the fragment and directs all output to the given Writer, or the
	 * JspWriter returned by the getOut() method of the JspContext associated
	 * with the fragment if out is null.
	 * 
	 * @param out
	 *            The Writer to output the fragment to, or null if output should
	 *            be sent to JspContext.getOut().
	 * @throws javax.servlet.jsp.JspException
	 *             Thrown if an error occured while invoking this fragment.
	 * @throws javax.servlet.jsp.SkipPageException
	 *             Thrown if the page that (either directly or indirectly)
	 *             invoked the tag handler that invoked this fragment is to
	 *             cease evaluation. The container must throw this exception if
	 *             a Classic Tag Handler returned Tag.SKIP_PAGE or if a Simple
	 *             Tag Handler threw SkipPageException.
	 * @throws java.io.IOException
	 *             If there was an error writing to the stream.
	 */
	public abstract void invoke(Writer out) throws JspException, IOException;

	/**
	 * Returns the JspContext that is bound to this JspFragment.
	 * 
	 * @return The JspContext used by this fragment at invocation time.
	 */
	public abstract JspContext getJspContext();

}
